From ef7a79488a498b430108a1d74647f57da9a78284 Mon Sep 17 00:00:00 2001 From: Prakash Surya Date: Mon, 8 Jan 2018 13:45:53 -0800 Subject: [PATCH] OpenZFS 8997 - ztest assertion failure in zil_lwb_write_issue PROBLEM ======= When `dmu_tx_assign` is called from `zil_lwb_write_issue`, it's possible for either `ERESTART` or `EIO` to be returned. If `ERESTART` is returned, this will cause an assertion to fail directly in `zil_lwb_write_issue`, where the code assumes the return value is `EIO` if `dmu_tx_assign` returns a non-zero value. This can occur if the SPA is suspended when `dmu_tx_assign` is called, and most often occurs when running `zloop`. If `EIO` is returned, this can cause assertions to fail elsewhere in the ZIL code. For example, `zil_commit_waiter_timeout` contains the following logic: lwb_t *nlwb = zil_lwb_write_issue(zilog, lwb); ASSERT3S(lwb->lwb_state, !=, LWB_STATE_OPENED); In this case, if `dmu_tx_assign` returned `EIO` from within `zil_lwb_write_issue`, the `lwb` variable passed in will not be issued to disk. Thus, it's `lwb_state` field will remain `LWB_STATE_OPENED` and this assertion will fail. `zil_commit_waiter_timeout` assumes that after it calls `zil_lwb_write_issue`, the `lwb` will be issued to disk, and doesn't handle the case where this is not true; i.e. it doesn't handle the case where `dmu_tx_assign` returns `EIO`. SOLUTION ======== This change modifies the `dmu_tx_assign` function such that `txg_how` is a bitmask, rather than of the `txg_how_t` enum type. Now, the previous `TXG_WAITED` semantics can be used via `TXG_NOTHROTTLE`, along with specifying either `TXG_NOWAIT` or `TXG_WAIT` semantics. Previously, when `TXG_WAITED` was specified, `TXG_NOWAIT` semantics was automatically invoked. This was not ideal when using `TXG_WAITED` within `zil_lwb_write_issued`, leading the problem described above. Rather, we want to achieve the semantics of `TXG_WAIT`, while also preventing the `tx` from being penalized via the dirty delay throttling. With this change, `zil_lwb_write_issued` can acheive the semtantics that it requires by passing in the value `TXG_WAIT | TXG_NOTHROTTLE` to `dmu_tx_assign`. Further, consumers of `dmu_tx_assign` wishing to achieve the old `TXG_WAITED` semantics can pass in the value `TXG_NOWAIT | TXG_NOTHROTTLE`. Authored by: Prakash Surya Approved by: Robert Mustacchi Reviewed by: Matt Ahrens Reviewed by: Andriy Gapon Ported-by: Brian Behlendorf Porting Notes: - Additionally updated `zfs_tmpfile` to use `TXG_NOTHROTTLE` OpenZFS-issue: https://www.illumos.org/issues/8997 OpenZFS-commit: https://github.com/openzfs/openzfs/commit/19ea6cb0f9 Closes #7084 --- include/sys/dmu.h | 15 ++++++----- include/sys/dmu_tx.h | 8 +++--- module/zfs/dmu_tx.c | 57 ++++++++++++++++++++++-------------------- module/zfs/zfs_vnops.c | 21 ++++++++-------- module/zfs/zil.c | 10 +++++++- 5 files changed, 63 insertions(+), 48 deletions(-) diff --git a/include/sys/dmu.h b/include/sys/dmu.h index 755a90561a..5b355afb90 100644 --- a/include/sys/dmu.h +++ b/include/sys/dmu.h @@ -227,11 +227,14 @@ typedef enum dmu_object_type { DMU_OTN_ZAP_METADATA = DMU_OT(DMU_BSWAP_ZAP, B_TRUE), } dmu_object_type_t; -typedef enum txg_how { - TXG_WAIT = 1, - TXG_NOWAIT, - TXG_WAITED, -} txg_how_t; +/* + * These flags are intended to be used to specify the "txg_how" + * parameter when calling the dmu_tx_assign() function. See the comment + * above dmu_tx_assign() for more details on the meaning of these flags. + */ +#define TXG_NOWAIT (0ULL) +#define TXG_WAIT (1ULL<<0) +#define TXG_NOTHROTTLE (1ULL<<1) void byteswap_uint64_array(void *buf, size_t size); void byteswap_uint32_array(void *buf, size_t size); @@ -694,7 +697,7 @@ void dmu_tx_hold_spill(dmu_tx_t *tx, uint64_t object); void dmu_tx_hold_sa(dmu_tx_t *tx, struct sa_handle *hdl, boolean_t may_grow); void dmu_tx_hold_sa_create(dmu_tx_t *tx, int total_size); void dmu_tx_abort(dmu_tx_t *tx); -int dmu_tx_assign(dmu_tx_t *tx, enum txg_how txg_how); +int dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how); void dmu_tx_wait(dmu_tx_t *tx); void dmu_tx_commit(dmu_tx_t *tx); void dmu_tx_mark_netfree(dmu_tx_t *tx); diff --git a/include/sys/dmu_tx.h b/include/sys/dmu_tx.h index d82a79310d..74b7e11163 100644 --- a/include/sys/dmu_tx.h +++ b/include/sys/dmu_tx.h @@ -67,9 +67,6 @@ struct dmu_tx { /* placeholder for syncing context, doesn't need specific holds */ boolean_t tx_anyobj; - /* has this transaction already been delayed? */ - boolean_t tx_waited; - /* transaction is marked as being a "net free" of space */ boolean_t tx_netfree; @@ -79,6 +76,9 @@ struct dmu_tx { /* need to wait for sufficient dirty space */ boolean_t tx_wait_dirty; + /* has this transaction already been delayed? */ + boolean_t tx_dirty_delayed; + int tx_err; }; @@ -138,7 +138,7 @@ extern dmu_tx_stats_t dmu_tx_stats; * These routines are defined in dmu.h, and are called by the user. */ dmu_tx_t *dmu_tx_create(objset_t *dd); -int dmu_tx_assign(dmu_tx_t *tx, txg_how_t txg_how); +int dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how); void dmu_tx_commit(dmu_tx_t *tx); void dmu_tx_abort(dmu_tx_t *tx); uint64_t dmu_tx_get_txg(dmu_tx_t *tx); diff --git a/module/zfs/dmu_tx.c b/module/zfs/dmu_tx.c index c3cc03a691..6ebff26714 100644 --- a/module/zfs/dmu_tx.c +++ b/module/zfs/dmu_tx.c @@ -854,7 +854,7 @@ dmu_tx_delay(dmu_tx_t *tx, uint64_t dirty) * decreasing performance. */ static int -dmu_tx_try_assign(dmu_tx_t *tx, txg_how_t txg_how) +dmu_tx_try_assign(dmu_tx_t *tx, uint64_t txg_how) { spa_t *spa = tx->tx_pool->dp_spa; @@ -878,13 +878,13 @@ dmu_tx_try_assign(dmu_tx_t *tx, txg_how_t txg_how) * of the failuremode setting. */ if (spa_get_failmode(spa) == ZIO_FAILURE_MODE_CONTINUE && - txg_how != TXG_WAIT) + !(txg_how & TXG_WAIT)) return (SET_ERROR(EIO)); return (SET_ERROR(ERESTART)); } - if (!tx->tx_waited && + if (!tx->tx_dirty_delayed && dsl_pool_need_dirty_delay(tx->tx_pool)) { tx->tx_wait_dirty = B_TRUE; DMU_TX_STAT_BUMP(dmu_tx_dirty_delay); @@ -976,41 +976,44 @@ dmu_tx_unassign(dmu_tx_t *tx) } /* - * Assign tx to a transaction group. txg_how can be one of: + * Assign tx to a transaction group; txg_how is a bitmask: * - * (1) TXG_WAIT. If the current open txg is full, waits until there's - * a new one. This should be used when you're not holding locks. - * It will only fail if we're truly out of space (or over quota). + * If TXG_WAIT is set and the currently open txg is full, this function + * will wait until there's a new txg. This should be used when no locks + * are being held. With this bit set, this function will only fail if + * we're truly out of space (or over quota). * - * (2) TXG_NOWAIT. If we can't assign into the current open txg without - * blocking, returns immediately with ERESTART. This should be used - * whenever you're holding locks. On an ERESTART error, the caller - * should drop locks, do a dmu_tx_wait(tx), and try again. + * If TXG_WAIT is *not* set and we can't assign into the currently open + * txg without blocking, this function will return immediately with + * ERESTART. This should be used whenever locks are being held. On an + * ERESTART error, the caller should drop all locks, call dmu_tx_wait(), + * and try again. * - * (3) TXG_WAITED. Like TXG_NOWAIT, but indicates that dmu_tx_wait() - * has already been called on behalf of this operation (though - * most likely on a different tx). + * If TXG_NOTHROTTLE is set, this indicates that this tx should not be + * delayed due on the ZFS Write Throttle (see comments in dsl_pool.c for + * details on the throttle). This is used by the VFS operations, after + * they have already called dmu_tx_wait() (though most likely on a + * different tx). */ int -dmu_tx_assign(dmu_tx_t *tx, txg_how_t txg_how) +dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how) { int err; ASSERT(tx->tx_txg == 0); - ASSERT(txg_how == TXG_WAIT || txg_how == TXG_NOWAIT || - txg_how == TXG_WAITED); + ASSERT0(txg_how & ~(TXG_WAIT | TXG_NOTHROTTLE)); ASSERT(!dsl_pool_sync_context(tx->tx_pool)); - if (txg_how == TXG_WAITED) - tx->tx_waited = B_TRUE; - /* If we might wait, we must not hold the config lock. */ - ASSERT(txg_how != TXG_WAIT || !dsl_pool_config_held(tx->tx_pool)); + IMPLY((txg_how & TXG_WAIT), !dsl_pool_config_held(tx->tx_pool)); + + if ((txg_how & TXG_NOTHROTTLE)) + tx->tx_dirty_delayed = B_TRUE; while ((err = dmu_tx_try_assign(tx, txg_how)) != 0) { dmu_tx_unassign(tx); - if (err != ERESTART || txg_how != TXG_WAIT) + if (err != ERESTART || !(txg_how & TXG_WAIT)) return (err); dmu_tx_wait(tx); @@ -1054,12 +1057,12 @@ dmu_tx_wait(dmu_tx_t *tx) tx->tx_wait_dirty = B_FALSE; /* - * Note: setting tx_waited only has effect if the caller - * used TX_WAIT. Otherwise they are going to destroy - * this tx and try again. The common case, zfs_write(), - * uses TX_WAIT. + * Note: setting tx_dirty_delayed only has effect if the + * caller used TX_WAIT. Otherwise they are going to + * destroy this tx and try again. The common case, + * zfs_write(), uses TX_WAIT. */ - tx->tx_waited = B_TRUE; + tx->tx_dirty_delayed = B_TRUE; } else if (spa_suspended(spa) || tx->tx_lasttried_txg == 0) { /* * If the pool is suspended we need to wait until it diff --git a/module/zfs/zfs_vnops.c b/module/zfs/zfs_vnops.c index 34ea751c32..4805f89772 100644 --- a/module/zfs/zfs_vnops.c +++ b/module/zfs/zfs_vnops.c @@ -129,7 +129,7 @@ * * If dmu_tx_assign() returns ERESTART and zfsvfs->z_assign is TXG_NOWAIT, * then drop all locks, call dmu_tx_wait(), and try again. On subsequent - * calls to dmu_tx_assign(), pass TXG_WAITED rather than TXG_NOWAIT, + * calls to dmu_tx_assign(), pass TXG_NOTHROTTLE in addition to TXG_NOWAIT, * to indicate that this operation has already called dmu_tx_wait(). * This will ensure that we don't retry forever, waiting a short bit * each time. @@ -154,7 +154,7 @@ * rw_enter(...); // grab any other locks you need * tx = dmu_tx_create(...); // get DMU tx * dmu_tx_hold_*(); // hold each object you might modify - * error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + * error = dmu_tx_assign(tx, (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); * if (error) { * rw_exit(...); // drop locks * zfs_dirent_unlock(dl); // unlock directory entry @@ -1427,7 +1427,8 @@ top: dmu_tx_hold_write(tx, DMU_NEW_OBJECT, 0, acl_ids.z_aclp->z_acl_bytes); } - error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + error = dmu_tx_assign(tx, + (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); if (error) { zfs_dirent_unlock(dl); if (error == ERESTART) { @@ -1602,7 +1603,7 @@ top: dmu_tx_hold_write(tx, DMU_NEW_OBJECT, 0, acl_ids.z_aclp->z_acl_bytes); } - error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + error = dmu_tx_assign(tx, (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); if (error) { if (error == ERESTART) { waited = B_TRUE; @@ -1775,7 +1776,7 @@ top: */ dmu_tx_mark_netfree(tx); - error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + error = dmu_tx_assign(tx, (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); if (error) { zfs_dirent_unlock(dl); if (error == ERESTART) { @@ -2017,7 +2018,7 @@ top: dmu_tx_hold_sa_create(tx, acl_ids.z_aclp->z_acl_bytes + ZFS_SA_BASE_ATTR_SIZE); - error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + error = dmu_tx_assign(tx, (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); if (error) { zfs_dirent_unlock(dl); if (error == ERESTART) { @@ -2156,7 +2157,7 @@ top: zfs_sa_upgrade_txholds(tx, zp); zfs_sa_upgrade_txholds(tx, dzp); dmu_tx_mark_netfree(tx); - error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + error = dmu_tx_assign(tx, (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); if (error) { rw_exit(&zp->z_parent_lock); rw_exit(&zp->z_name_lock); @@ -3623,7 +3624,7 @@ top: zfs_sa_upgrade_txholds(tx, szp); dmu_tx_hold_zap(tx, zfsvfs->z_unlinkedobj, FALSE, NULL); - error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + error = dmu_tx_assign(tx, (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); if (error) { if (zl != NULL) zfs_rename_unlock(&zl); @@ -3815,7 +3816,7 @@ top: } if (fuid_dirtied) zfs_fuid_txhold(zfsvfs, tx); - error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + error = dmu_tx_assign(tx, (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); if (error) { zfs_dirent_unlock(dl); if (error == ERESTART) { @@ -4041,7 +4042,7 @@ top: zfs_sa_upgrade_txholds(tx, szp); zfs_sa_upgrade_txholds(tx, dzp); - error = dmu_tx_assign(tx, waited ? TXG_WAITED : TXG_NOWAIT); + error = dmu_tx_assign(tx, (waited ? TXG_NOTHROTTLE : 0) | TXG_NOWAIT); if (error) { zfs_dirent_unlock(dl); if (error == ERESTART) { diff --git a/module/zfs/zil.c b/module/zfs/zil.c index 645b1d4d80..a2bbdcb9aa 100644 --- a/module/zfs/zil.c +++ b/module/zfs/zil.c @@ -1009,7 +1009,15 @@ zil_lwb_write_start(zilog_t *zilog, lwb_t *lwb) * to clean up in the event of allocation failure or I/O failure. */ tx = dmu_tx_create(zilog->zl_os); - VERIFY(dmu_tx_assign(tx, TXG_WAIT) == 0); + + /* + * Since we are not going to create any new dirty data, and we + * can even help with clearing the existing dirty data, we + * should not be subject to the dirty data based delays. We + * use TXG_NOTHROTTLE to bypass the delay mechanism. + */ + VERIFY0(dmu_tx_assign(tx, TXG_WAIT | TXG_NOTHROTTLE)); + dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx); txg = dmu_tx_get_txg(tx);